High-oxygen-demand strains are those that require large amounts of oxygen during their growth and metabolism. These strains are highly efficient in oxygen consumption and are commonly used in genetically engineered bacteria for industrial applications requiring high-oxygen environments, such as biodegradation and wastewater treatment. For example, Bacillus subtilis, a typical high-oxygen-consuming strain, rapidly consumes oxygen in wastewater treatment, effectively decomposing organic pollutants and significantly reducing the chemical oxygen demand of water. Its high oxygen consumption makes it an important microbial resource in environmental protection.
Microorganisms sensitive to shear forces include the following categories:
a. Plant cells: Due to their rigid and fragile cell walls and large vacuoles, plant cells are relatively sensitive to shear force. Appropriate shear force can promote cell growth and enhance metabolism, but excessive shear force may cause mechanical damage, reduce cell activity, or disrupt the cell membrane structure, thereby affecting cell growth and metabolism. For example, safflower cells (Carthamus tinctorius L.) have a low tolerance to shear force; when it exceeds a certain threshold, cell growth and metabolism are affected.
b. Mammalian cells: Mammalian cells lack a cell wall, and their membranes are relatively fragile and susceptible to external mechanical forces. Their large size also makes them more sensitive to shear forces.
c. Aspergillus niger in citric acid fermentation: As the primary producer of citric acid, Aspergillus niger is a shear-sensitive microorganism. Its morphological characteristics significantly affect citric acid yield. Excessive shear force may impair its growth and metabolism, reducing citric acid yield.
d. Cells at different growth stages: Plant cells respond differently to shear force at different growth stages. For example, taxus cells in the logarithmic phase are highly sensitive to shear forces.
The effect of shear force on microorganisms is complex, depending on species, growth stage, and factors such as intensity, duration, and environmental conditions. In practice, shear force must be controlled and optimized to ensure optimal microbial growth and metabolism.
Prokaryotic microbes lack true nuclei and organelles such as the endoplasmic reticulum and Golgi apparatus, limiting their ability and speed in post-translational protein modification and secretion. Therefore, the expression process must be carefully controlled.
Processes such as fed-batch, temperature-sensitive strains, induction, mixed fermentation, oxygen switching, and substrate switching require segmented design, with speed control at specific stages to ensure optimal growth and metabolic conditions.